May deluge could help bay recuperate
May 30, 2018
SOUTH FLORIDA — Rains washed out many Memorial Day holiday plans, but May’s record-setting month of wet could make for a healthier Florida Bay.
Even before Tropical Storm Alberto added its weekend deluge, seemingly incessant rains went a long way to reduce the shallow bay’s salinity, several experts said.
“This rain certainly is welcome to help rehydrate Everglades National Park and Florida Bay,” Stephen Davis, a wetland ecologist with the Everglades Foundation, said. “We’re going to see the benefits of the freshening throughout the park and Florida Bay.”
Among those benefits may be a much reduced chance of harmful algal blooms in the hot summer months.
“The system has kind of rebounded,” said Randy Smith, South Florida Water Management District spokesman. “It’s not that we want to see that much water in Lake Okeechobee, but [the rainfall] is a silver lining for a lot of the Everglades system and Florida Bay.”
Several Florida Bay basins that had disturbingly high salinity levels are dropping toward a normal range, which helps to discourage fish-killing blooms.
It has been a rough decade for Florida Bay. The 2015 drought helped trigger a massive 2016 seagrass dieoff that destroyed tens of thousands of acres. Scientists estimate seagrass recovery may take 20 years.
That decaying seagrass sucked dissolved oxygen out of the system, leading to poor water visibility that hinders seagrass regrowth and higher chlorophyll levels that heighten the threat of harmful algae blooms.
In Garfield Bight, a shallow basin east of Flamingo, salinity levels previously have reached 70 parts per thousand (ppt), said South Florida Natural Resources Center Director Robert Johnson.
Ocean water typically is 35 parts per thousand, and Florida Bay historically is less saline than the ocean.
“Every year, there’s a bull’s-eye around Garfield Bight, Terrapin Bay and Rankin Bight,” Johnson said. “These basins are so shallow that it’s like a big evaporating dish.”
“A combination of evaporation and a lack of rainfall,” he said, then leads to “hypersaline” conditions.
Bay conditions seemed to be improving somewhat in 2017. Then Hurricane Irma arrived, pushing staggering amounts of uprooted seagrass into the bay.
“The floating seagrass looked reddish because Irma tore it loose from the bottom. The grass was floating upside down with roots on top,” Johnson said. Reports of blooms followed in October and November as that vegetation decayed.
The winter’s dry season caused salinity levels to rise along the Florida Bay coastline north of the Florida Keys.
Parts of the northern bay had salinity levels in the 40-plus ppt range in April but had dropped by 10 ppt or more in late May. That was before Alberto sloshed through.
Seagrasses become stressed at 55 ppt, Johnson said.
Some of the recently finished Everglades restoration projects also are having a beneficial effect, said Johnson, whose agency provides research for South Florida’s national parks.
The recent improvement in the system “has been very much rain driven,” he said, “but during the dry delivery periods, you can’t argue that [restoration] is not helping.”
“The freshening effect is extending into the bay, all way down to around Butternut Key,” Johnson said.
Completion of more projects remains critical, he said.
“What’s happening now is promising, and we’ll build on it when the other projects come on line,” he said. “By 2020, we should see some real progress.”